Biometric authentication systems that perform human authentication using biometric data are used in various situations. In the following, a description is given based on, for example, a client/server system where biometric data are acquired on the client side and biometric data for reference are retained and collation is performed on the server side at the time of authentication. However, this does not exclude, as an object of application, a stand-alone system where biometric data are acquired and collated in a single apparatus. Further, a description is given based on, for example, a system where a user specifies her/his identifier (ID) and collation is performed with one or more biometric data items for reference identified by the user's ID at the time of authentication. However, this does not exclude, as an object of application, a system where collation is performed with a group of candidate biometric data for reference without specification of an ID by a user.
In this type of biometric authentication system, a user pre-registers her/his biometric data obtained from a specific part of her/his living body with the database of a server for reference purposes. At this point, it is recommended that biometric data taken not from a single part but from two or more parts of the living body be registered so that even if a part of the living body usually used for authentication is hurt and not usable, authentication may be performed with another part of the living body. For example, with respect to an iris, biometric data taken from the right and left eyes are registered as data. With respect to palm veins, biometric data taken from the right and left hands are registered as data. In the case of fingerprints or finger veins, an extra finger may be registered in addition to a finger usually used or all fingers (ten fingers) may be registered so that any finger may be used.
Thus, registration of the biometric data of living body parts other than that usually used allows a user to be authenticated by using another registered living body part even if the living body part usually used for authentication is hurt. Further, by thus registering multiple biometric data items, authentication may be performed with any finger in the case of fingerprints, for example, thus producing an advantage in terms of convenience as well.
However, on the server side where authentication is processed, the biometric data item entered by a person for collation is collated with all the registered biometric data items of the person as long as a part to be used is not clearly specified. In this case, practically, the relationship between an entered item and corresponding processing on the server side is not 1:1 but 1:2 or more even if collation is performed with the person specified with her/his ID. In the case of a fingerprint authentication system that recommends registration of ten fingers, this ratio is 1:10.
Time for this processing is not so conspicuous if a biometric authentication algorithm that enables high-speed processing is employed. For example, if a biometric authentication algorithm is employed that processes one collation at high speed in 1 ms (0.001 s), execution of 1:10 processing does not cause much trouble because the time required for collating one person is 10 ms. Nowadays, however, the number of systems operating on a large scale with tens or hundreds of thousands of people to be processed is also increasing. In such systems, all system users may be subjected to personal authentication substantially at the same time at the start of office hours or at the end of a break. In the case of a fingerprint authentication system recommending ten-finger registration, if the system processes ten thousand people, there is a processing time of 10 ms×ten thousand people=100 s (approximately 1.67 minutes) before completion of the entire processing even with a high-speed biometric authentication algorithm that processes one collation in 1 ms as described above. It is possible to reduce processing time by adding a processing server or improving CPU performance. This, however, incurs apparatus expenses. Further, this is also inefficient in performing collation that is unnecessary in nature.
Solutions to such problems include such a technique as disclosed in Japanese Laid-Open Patent Publication No. 2007-122529, which is related to a biometric authentication system used in automated teller machines (ATMs) and the like. According to Japanese Laid-Open Patent Publication No. 2007-122529, the number of successful collations is counted every time biometric information collation is performed, and the order of priorities of multiple prestored biometric information items is changed in accordance with their numbers of successful collations. Thus, multiple biometric information items are prioritized in accordance with their numbers of successes of collation, the biometric information items are subjected to authentication (collation) in order of descending priorities, and a person is authenticated and the processing ends in response to detection of a match. As a result, personal authentication may be performed in a short processing time without performing unnecessary collation.